Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1997-06-02
2002-08-06
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S281000, C156S307500, C156S316000, C428S416000
Reexamination Certificate
active
06428645
ABSTRACT:
TECHNICAL FIELD
This invention pertains to vehicular mounting or cushioning assemblies involving a resilient rubber or elastomeric body that is adhesively bonded to a bracket or containment member.
BACKGROUND OF THE INVENTION
There are several applications in automobile technology in which a cushioning or mounting member is employed to support an engine or a transmission to body members or to provide a cushioned connection (e.g., a bushing) between suspension members. A typical engine mount or transmission mount, for example, employs a resilient body of polyisoprene rubber, or such rubber mixed with other suitable elastomer material, sandwiched, sometimes under pressure, between cooperating bracket members. One of the bracket members is connected to the engine or to the transmission, and another bracket member is attached to a vehicle body member. In addition to being sandwiched and sometimes compressed between the bracket members, the rubber or other elastomer is adhesively bonded to the brackets.
The bonding requirement in such an application can vary from structural to nonstructural. In structural bonding, where the bond is expected to sustain a substantial load, the bond is considered successful if the entire bracket or substrate is covered with torn rubber after failure of the test specimen. In nonstructural bonding, the rubber-bracket interface is not subjected to large tensile or shear loads. It is only necessary to keep the rubber in intimate contact with the bracket. The bracket is usually, but not necessarily always, steel or aluminum.
The techniques employed for such rubber bonding are divided naturally depending on whether the bond is made while the rubber cures, in situ bonding, or after cure, post-vulcanization bonding. In situ bonding is the accepted method for the manufacture of many natural or synthetic polyisoprene rubber bonded articles such as mounting devices where a rigid insert, commonly a steel tube, is substantially surrounded by a body of rubber. An adhesive is first coated on the rigid insert from a solvent or water carrier and then dried. The insert is then placed like a core member in the rubber mold prior to injection of the uncured rubber. Adhesive cure takes place during the rubber curing process. Examples of suitable adhesives for in situ or pre-vulcanization are the reactive elastomeric products sold under the trade names of Chemlok™ and Thixon™, respectively, by Lord Corporation and Morton International in the United States. Such in situ bonds are usually stronger than post-vulcanization bonds.
A number of techniques are used for post-vulcanization bonding. A most common practice utilizes the same type of reactive elastomeric adhesive used for in situ bonding. In this case, the cured rubber mass is held in contact with the adhesive coated surface and heated. Substantial pressure is required, often requiring the rubber to be compressed by about 20% of its original height. This method is particularly attractive for products such as bonded bushings where a cylindrical mass of rubber is compressed within an annular outer shell. The pressure requirement is easily met by the rubber being captured within the outer shell.
The use of epoxy resin in the manufacture of vehicular powertrain mounts was taught as an alternative to reactive elastomeric adhesives for post-vulcanization bonding in U.S. Pat. Nos. 4,987,679 and 5,031,873, assigned to the assignee of this invention. This process utilizes a two-component epoxy adhesive to bond cured rubber to rigid inserts. The primary advantage of the epoxy adhesive over conventional post-vulcanization bonding using reactive elastomeric adhesives is that pressure is not required to achieve good bonds. Also, a fair amount of mismatch between the rubber and the rigid insert can be tolerated since the mixed but uncured epoxy is mobile and fills gaps and still bonds well. This technology has made it attractive to convert designs that would otherwise be bonded in situ. It is not necessarily attractive for applications such as bushings where the rubber mass must be pushed into a constrictive shell. The uncured epoxy on the bond surface of the shell tends to be wiped out during rubber insertion, resulting in weak bonds.
Several production powertrain mounts are currently manufactured utilizing such two-part epoxy adhesives. In these applications, an electrophoretically-deposited cathodic resin is used on the surfaces of the metal bracket for the dual purpose of providing a primer for the epoxy adhesive as well as providing required corrosion protection in areas not bonded. The cathodic primer is usually applied over a zinc phosphate coating (actually a mixed zinc-iron phosphate) integral with the surface of the steel bracket.
The cathodic, electrophoretically-deposited coat is actually a single epoxy resin component paint which is electrolytically deposited from an aqueous bath. After the coating application or electroplating of the cathodic electrophoretic epoxy paint, the coated metal parts are cured at temperatures of 350° F. to 450° F. to convert the epoxy coating into a tough chemical and environmentally-resistant coating. In other words, the coating is cured or crosslinked. Such coatings are now used widely in the production of automotive bodies where the entire body is dipped into a tank and primed as a unit. Exemplary electrophoretically-applied epoxy paints are manufactured and sold by companies such as PPG under trade names such as Powercron 500™ and Powercron 640™. Electrophoretically-deposited epoxy paints are baked after application at temperatures of the order of 400° F. until they are cured. In their baked condition, they are scratch resistant and resistant to solvents such as gasoline or automobile oils. In the case of body parts, uncured paints are sprayed onto the primed surface and later baked to dry the paints. In the case of the above-mentioned engine or transmission mount applications (i.e., the '679 and '873 patent disclosures), a two-part epoxy adhesive is applied on top of the epoxy prime coat for the purpose of bonding the rubber-cushion body to the primed metal surface.
It is, of course, always of interest to simplify and render less complicated and expensive the practice of bonding a cured rubber body to a support bracket in a vehicle mount application and in other applications.
SUMMARY OF THE INVENTION
This invention is based on the discovery that it is possible to eliminate the epoxy adhesive as described in the above '679 and '873 patents and bond vulcanized polyisoprene rubber directly to a baked electrophoretically-applied epoxy prime coat material. In a more general statement of the invention, it has been found that it is possible by application of suitable pressure and heat to bond cured rubber containing 40% by weight or more natural or synthetic polyisoprene to a baked or cured epoxy resin-coated mounting device surface. This results in an excellent bond between the bulk elastomer and a bracket member which is capable of sustaining the loads that are common in vehicle mount applications and the like.
A preferred application of the invention is the bonding of natural rubber to an electrophoretically-applied epoxy resin prime-coated bracket. After the prime-coated bracket has been baked, for example, at a temperature of 350° F. to 450° F., to convert the coating into a tough, chemical- and environmentally-resistant coating, the bracket is ready to serve as a bonding surface for the resilient natural rubber body. The surface of the rubber body is chlorinated by immersing the bulk rubber in, for example, an aqueous solution of acidified sodium hypochlorite. The chlorinated surface rubber body is then pressed against the baked epoxy prime coat and the assembly heated to a temperature of the order of 250° F. to 350° F. for 15 minutes or so to form a strong bond between the chlorinated natural rubber surface and the epoxy prime coat.
As will be discussed below, this practice may be utilized with other suitable bulk resilient polyisoprene-containing elastomeric bodies an
Delphi Technologies Inc.
Gallagher John J.
Sigler Robert M.
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